The present invention relates to the fabrication of sandwich type structural materials, particularly to the fabrication of light weight core material of the sandwich type, and more particularly to a method for fabricating a core material pattern which utilizes star shaped cells.
Sandwich constructions involve a light weight core material that supports the faces and transfers load between them. The sandwich constructions generally utilize low density core materials. The elastic mechanical behavior for low density materials allows for deformation due to the flexibility of the core material when utilized in sandwich type constructions.
The traditional core material is of a triangular cell pattern, and more recently of a honeycomb (hexagonal) cell pattern. However, the triangular or hexagonal cell patterns of core materials do not easily conform to curved shapes needed to fabricate curved sandwich material panels. Thus, there has been a need for a core material which supports the faces of the sandwich construction materials on transfer loads between the faces, while being sufficiently flexible so as to conform easily to curved shapes. That need has been satisfied by the invention described and claimed in above-identified U.S. Pat. No. 5,437,903, which involves an improved microstructure for light weight core material utilizing a star/hexagonal pattern which allows easy conformation to curved shapes.
Various fabrication processes have been developed for the cellular sandwich structural materials, in an effort to produce these materials at a reasonable cost. For example, the prior honeycomb (hexagonal) material is fabricated by first vertically stacking a series of flat sheets with bonds located at the points of interconnection between the hexagonal cells, honeycomb configuration. The present invention, involving a method for fabricating an improved microstructure for light weight core material using the star containing pattern of the above-identified patent, utilizes features of the prior known processes by bonding or welding folded or unfolded sheets of material at selected locations to interconnect the sheets in both a vertical and a horizontal direction, and then mechanically pulling the interconnected sheets normal to the plane of the sheets which expands the sheets and form the star cells.